The European Union has backed a "strong response" to the chemical attack near Damascus.

Reuters: Bassam Khabieh

European Union foreign ministers have urged "a clear and strong response" to an alleged Syria chemical weapons attack while stopping short of endorsing a strike on the Damascus regime.

Speaking after the bloc's 28 ministers held talks with US secretary of state John Kerry, the EU's foreign policy chief Catherine Ashton read out a statement saying the ministers "were unanimous in condemning in the strongest terms this horrific attack."

Dubbing the August 21 attack outside Damascus that left hundreds dead "a war crime and a crime against humanity", the statement said there was "strong evidence that the Syrian regime (of President Bashar al-Assad) is responsible."

"The international community cannot remain idle," it added.

"A clear and strong response is critical to make clear that such crimes are unacceptable and that there can be no impunity."

On leaving the Lithuanian capital for talks in Paris, Mr Kerry welcomed the "strong statement about the need for accountability ... that support the efforts to hold the Assad regime accountable for what he's done."

Europe has been sharply divided over how to respond to US calls for military action against Syria after the attack which Washington, Paris and London claim was carried out by the Assad regime.

The EU statement agreed after two days of informal talks stressed that there could be no end to the long and bloody Syrian war without a political solution.

It also urged the UN Security Council "to fulfil its responsibilities", a clear reference to Russia and China's refusal to sanction Assad.

France is the sole EU nation currently willing to take part in a US-led intervention, with most of the bloc's governments reluctant to offer even political backing for military action without at best a UN mandate, or at least until the release of a much-awaited UN probe on the attack.

Ms Ashton said that EU ministers welcomed French president Francois Hollande's decision to await the release of the UN investigation before taking action against Syria.

But Mr Kerry made clear to the EU ministers that Washington had not decided to postpone a decision on military action until the release of the UN report.

"Secretary Kerry made clear that he would report back to the national security team the recommendations of some members of the EU to wait for the results of the UN inspection, but he also made clear that the United States has not made the decision to wait," a US State Department official said in response to media reports in Europe.

Germany meanwhile announced it has signed on to a global statement urging "a strong response" to the chemical weapons attack.

That made Germany the fifth EU member to back the statement issued at a G20 summit in Saint Petersburg on Friday and signed by 11 countries - including the US, Britain, France, Italy and Spain.

"After the Europeans found a common position here ... the chancellor and I decided that we can agree to the declaration which was made yesterday in Saint Petersburg," German foreign minister Guido Westerwelle said.

Mr Westerwelle has urged the UN to publish its chemical weapons report "as quickly as possible" to help Europe's divided leaders determine a joint response.